Radar and time-gating are two conventional technologies that are employed for imaging through fog.
Radar may employ radio waves with long wavelengths at which fog is transparent. However, the long wavelengths may cause the radar to have spatial resolution that is so poor that it is hard or even impossible to classify objects, and the use cases may be limited to detection. Furthermore, at these long wavelengths, the optical contrast of the radar may be so poor that it is only possible to measure bulk properties of materials, and impossible for example to identify road lane marks and read road signs.
Time gating may image a far-away object through fog. To do so, time-gated measurements may be taken of visible light reflecting from a foggy scene. However, conventional time gating requires long integration times and prior knowledge of the scene depth map. Furthermore, conventional time gating rejects scattered photons during the measurement process. Because conventional time gating rejects a substantial amount of the optical signal, it operates at a low signal-to-noise ratio (SNR).